This invention relates to display devices, such as field emission displays, plasma displays, and flat panel cathode ray tubes. Specifically, the invention relates to a uniform emitter array for display devices, an etch mask used in making the same, and methods for making the emitter array and etch mask.
Display devices visually present information generated by computers and other electronic devices. One category of display devices is electron emitter apparatus, such as a cold cathode field emission display (FED). A FED uses electrons originating from one or more emitters on a baseplate (also known as the panel) to illuminate a luminescent display screen and generate an image. The emitters can be arranged in groups called pixels. A gate electrode, located near the emitter, and the baseplate are in electrical communication with a voltage source. Electrons are emitted when a sufficient voltage differential is established between the emitter and the gate electrode. The electrons strike a phosphor coating on the display screen releasing photons to generate a visual image.
As shown in drawing FIGS. 1 and 2, emitters have been formed by etching portions of silicon layer 100 using oxide etch mask 102. The etching process is anisotropic, removing portions of silicon layer 100 underlying oxide etch mask 102 as well as portions not underlying the etch mask, thereby forming emitter tips 104. See, for example, U.S. Pat. Nos. 5,676,853, 5,302,238, 5,312,514, 5,372,973, 5,532,177, and 5,391,259. In such processes, a higher degree of etching removes more of silicon layer 100, forming a shorter emitter tip. Conversely, a lower degree of etching removes less of silicon layer 100, forming a longer emitter tip.
High resolution displays yield brighter images on the display screen and are therefore in high demand. High resolution displays may be obtained by creating a focused electron beam which reduces off-angle beams and mislanded electrons and therefore yields a brighter image. One method of obtaining such a focused electron beam is to fabricate emitters with substantially similar heights. The voltage then applied to a gate electrode and such emitters extracts a high number of electrons since the distance between the gate electrode and the emitter is uniform. If the height of the emitters is not uniform throughout the panel, the distance between the gate electrode and the emitters can vary from one emitter to the next. When this occurs, the number of electrons and the direction of emission vary, yielding a dimmer image because fewer electrons strike the display screen in the same area.
A problem with conventional emitters arrayed on a panel has been the non-uniformity of the emitter height. Emitters are often longer in the interior of the panel and shorter in the periphery of the panel because of etching reactor design and etching reactor loading of panels. The design of etching reactors causes slower etching in the interior of the panel and quicker etching in the periphery of the panel. Etching reactor loadingxe2x80x94where etching is slower in the interior of the reactor because the etching process occurs in all directions and faster in the periphery of the reactor, especially the edges, because the etching does not occur in all directionsxe2x80x94also contributes to this non-uniformity. This non-uniformity of the emitter height, as discussed above, has contributed to dimmer images.
The present invention includes a method for making an emitter for a display device by providing a substrate, forming a conducting layer on the substrate, forming an emitting layer on the conducting layer, forming an etch mask with a controlled distribution of a plurality of mask sizes over the emitting layer, and forming at least one emitter by removing portions of the emitting layer using the etch mask. The controlled distribution of mask sizes may contain one mask size as a median mask size and an equal number of larger and smaller mask sizes, where every larger mask size has a corresponding smaller mask size with the average of the corresponding smaller and larger mask sizes being the median mask size. The resulting field emission display device contains a plurality of pixels, where each pixel has at least one emitter with a substantially similar height.
The present invention also includes a method for making an etch mask for a display device emitter and the etch mask produced by this method. The method is practiced by forming an etch mask layer over an emitting layer, forming a patterning layer having a controlled distribution of mask sizes over the etch mask layer, and forming the etch mask by removing portions of the etch mask layer using the controlled distribution of mask sizes in the patterning layer. The controlled distribution of mask sizes may contain one mask size as a median mask size and an equal number of larger and smaller mask sizes, where every larger mask size has a corresponding smaller mask size with the average of the corresponding smaller and larger mask sizes being the median mask size. The larger mask sizes are located primarily in the periphery of the etch mask, the smaller mask sizes are located primarily located in the interior, and the median mask size is located throughout the etch mask.
The present invention also includes an emitter array for a field emission display device containing a plurality of pixels where at least one emitter in every pixel is substantially the same height. The at least one emitter may have a size of about 1.6 microns. Preferably, all emitter heights may be within 0.15 microns of each other, or, in other words, the height of any one emitter differs no more than about ten percent (10%) from another.
The present invention compensates for the non-uniformity introduced into emitter heights during formation by etching, which causes over and under sharpening of tips and alters their emission properties. By providing more uniform emitter heights throughout the field emission display device, the present invention leads to better emission properties and a brighter image.